1. Field of the Invention
The present invention relates generally to archery bows and more particularly pertains to an improved compression molded archery bow limb and method for manufacturing the same.
2. Description of the Prior Art
Archery bow limbs are an important component of archery bows. Their function is to store energy when the archer draws the bow string rearwardly. Typically, the bow limbs are made of resilient material which will be flexed rearwardly, thus storing energy, as the bowstring is drawn. When the archer releases the bowstring, the bow limbs will return to their normal unflexed position, and the energy previously stored in the limbs will be released to the bowstring causing the nocked arrow to be propelled forwardly. Such archery bow limbs have been manufactured from reinforced glass fiber materials for a number of years. Early reinforced glass fiber limbs were formed by machining the limb profile entirely from a unitary molded block of reinforced fiberglass material. It was recognized, however, that besides being time consuming and expensive, the machining process also severed load bearing glass fiber strands. That resulted in weaker limbs that could not be flexed at high stress levels for the desired limb life cycles.
In response to the problem caused by machining the reinforced glass fiber material, processes were developed, such as disclosed in U.S. Pat. Nos. 4,649,889; 4,353,769; and 4,390,156, which permitted the limb profile, with the exception of the limb tip slots, to be directly molded. It was believed that it would not be practical to mold the limb tip slots (i.e., the slots within which the eccentric wheel cams of a compound bow are seated) because, for example, as was stated in U.S. Pat. No. 4,649,889, different bows may require different size wheel cams making the cost of the dies to produce different size wheel cams prohibitive.
Therefore, it has been customary in the prior art to form the limb tip slots by grinding away, rather than molding, the limb material in this area from the limb block to provide sufficient clearance to mount the the paricular size eccentric wheel or cam and cable system to the end of the limb. This results in fiber reinforcement in the limb tip slot area being cut away, and even when the tip slots are radiused properly it may fracture and/or cracking may occur at or near the base of the slot. In order to overcome this deficiency the prior art has resorted to a number of solutions involving various methods.
One such method is to increase the limb thickness around the base of the slot, thus reducing both the bending and shear stresses in this area, and reducing the tendency to fracture. This solution, however, increases the mass weight of the limb and detracts from the aesthetic appearance of the bow.
Another method has been to apply a reinforcement pad or layer of material over the tip slot area. The reinforcement material strengthens the area and serves to hold the severed fibers on the limb tension side in position with the severed fibers no longer being the outermost fibers. In this manner the severed fibers are under less stress.
A third method is to employ a compression fitting. In its simplest form, two discs are attached to the bow limb at the base of the tip slot. One disc includes a clearance hole and the other disc is threaded to accept a capscrew. A clearance hole is drilled through the limb at the base of the limb slot, and the discs are then attached to the limb, one above and one below, so that the limb is sandwiched therebetween. Tightening of the screw draws the two discs together to apply pressure to the limb material at the base of the slot. This action compresses the limb material in this area reducing the tendency of the fibers to lift or cracks to form. Additionally, these disc washers conceal any cracks that do in fact occur. This use of additional components, however, increases the assembly and material costs of the bow limb.